Device for measuring the intensity of a strong current passing through a wire

ABSTRACT

The device for measuring the intensity ( 1 ) of a strong current passing through a wire ( 1 ) comprises a magnetic sensor ( 2 ) in the form of a loop surrounding the wire ( 1 ), and a turn ( 3 ) of conductive material surrounding the wire ( 1 ) conducting a high-frequency counter-current, the intensity of which is adjusted to cancel the magnetic field (H) is characterized in that the turn ( 3 ) of conductive material is in short circuit and surrounds the magnetic sensor ( 2 ).

The present invention relates to a device for measuring the intensity ofa strong current passing through a wire.

The term “strong current” is used to mean any current with an intensitybetween 100 and 1000 A.

To measure such strong currents, it is normally the magnetic fieldgenerated around the wire conducting the current that is measured.

To obtain an accurate measurement of this magnetic field, a so-called“opposition” method is used.

This method consists in placing around the wire a winding conducting acurrent counter to the direction of the magnetic field, that is adjustedto cancel the magnetic field.

When the counter-current control loop is a system said to be sampled ata frequency F0, the components having frequencies greater than thefrequency F0 that are present in the current to be measured can createserious errors.

The purpose of the present invention is to create a device for measuringthe intensity of a strong current which can filter the abovementionedspurious components in order to obtain an accurate measurement of theintensity.

The subject of the invention is thus a device for measuring theintensity of a strong current passing through a wire, comprising amagnetic sensor in the form of a loop surrounding the wire, and a turnof conductive material surrounding the wire, conducting a high-frequencycounter-current, the intensity of which is adjusted to cancel themagnetic field.

According to the invention, this device is characterized in that theturn of conductive material is in short circuit and surrounds themagnetic sensor.

The turn of conductive material in short circuit is a closed turn.

The resistance R of the turn of conductive material in short circuit isadjusted to obtain an L/R filtering constant, L being the inductance ofthe turn.

This turn in short circuit conducting a high-frequency counter-current,thus forms a filter that can filter the spurious components of thecurrent to be measured.

Preferably, the turn is made of soft iron and is surrounded externallyby a copper jacket.

Such a turn also acts as a shield against the electromagnetic fieldsexternal to the device.

In a preferred embodiment of the invention, the turn includes,internally, a channel concentric with the torus of the turn, containingthe magnetic sensor.

The magnetic sensor can be a wire of nickel-iron alloy forming a closedloop and surrounded around its entire circumference by a coil that isformed by helical turns.

The measuring device according to the invention thus comprises a singlecomponent which incorporates the turn and the magnetic circuit.

Other features and advantages of the invention will become apparent fromthe description below.

In the appended drawings, given by way of non-limiting examples:

FIG. 1 shows, in partial cross section, a current measuring deviceaccording to the invention, in which the turn and the magnetic circuitare incorporated in a single component,

FIG. 2 shows the magnetic sensor which is also incorporated in thecomponent shown in FIG. 1.

The device represented in FIG. 1 for measuring the intensity I of astrong current passing through a wire 1, comprises a magnetic sensor 2in the form of a loop surrounding the wire 1, a turn 3 of conductivematerial surrounding the wire, conducting a high-frequencycounter-current, the intensity of which is adjusted to cancel themagnetic field H.

According to the invention, the turn 3 of conductive material is closedand therefore in short circuit, and it surrounds the magnetic sensor 2.

The resistance R of the turn 3 of conductive material in short circuitis adjusted so as to obtain an L/R filtering constant, L being theinductance of the turn 3.

In the example shown, the turn 3 is made of soft iron 4 and issurrounded externally by a copper jacket 5.

As indicated in FIG. 1, the turn 3 includes, internally, a channel 6that is concentric with the torus of the turn 3, containing the magneticsensor 2 represented in detail in FIG. 2.

FIG. 2 shows that the magnetic sensor 2 is a wire 7 of nickel-iron alloy(Mumetal) forming a closed loop and surrounded around its entirecircumference by a coil 8 formed by helical turns.

The measuring device that has just been described can, for example,present the following characteristics: wire diameter (withoutinsulation): 4 mm nature of the wire 1: copper internal diameter of thetoroidal turn 3: 15 mm  outer diameter of the turn 3: 45 mm  thicknessof the copper jacket 5: 2 mm width of the channel 6: 5 mm

There now follows a description of the operation of the measuring devicethat has just been described.

The current of intensity I passing through the wire 1 generates amagnetic field H around this wire.

The turn 3 in short circuit surrounding the wire conducts ahigh-frequency counter-current (for example 10 Hz), the effect of whichis to generate a magnetic field in a direction opposite to the field Hso as to cancel the latter.

The magnetic sensor 2 incorporated in the turn 3 is used to measure themagnetic field and therefore detect the nullity of this field. The valueof the intensity I is obtained by measuring the intensity of thecounter-current.

The turn 3 made of a soft-iron core 4 and an external copper jacket 5presents a resistance R and an inductance L that can be adjusted byconstruction to obtain the required L/R filtering constant.

The turn 3 in short circuit is thus used to filter the spuriousfrequencies by adjusting the cut-off frequency F1 of the filter byaltering the dimensioning of the elements 4 and 5. The frequency F1 ischosen between the required bandwidth of the sensor (10 Hz for example)and the sampling frequency F0 (10 kHz for example).

The high-frequency components that are not reduced by the compensatingcurrent no longer saturate the measurement subsystem. The detrimentalphase lag due to a magnetic signal filter is eliminated. Theanti-aliasing low-pass filter is outside the control loop.

1. A device for measuring the intensity (I) of a strong current passingthrough a wire (1), comprising a magnetic sensor (2) in the form of aloop surrounding the wire (1), and a turn (3) of conductive materialsurrounding the wire (1), conducting a high-frequency counter-current,the intensity of which is adjusted to cancel the magnetic field (H),characterized in that the turn (3) of conductive material is in shortcircuit and surrounds the magnetic sensor (2).
 2. The device as claimedin claim 1, characterized in that the turn (3) of conductive material inshort circuit is a closed turn.
 3. The device as claimed in claim 1,characterized in that the resistance R of the turn (3) of conductivematerial in short circuit is adjusted to obtain an L/R filteringconstant, L being the inductance of the turn (3).
 4. The device asclaimed in claim 2, characterized in that the turn (3) is made of softiron (4).
 5. The device as claimed in claim 4, characterized in that theturn (3) of soft iron (4) is surrounded externally by a copper jacket(5).
 6. The device as claimed in claim 2, characterized in that the turn(3) includes, internally, a channel (6) concentric with the torus of theturn, containing the magnetic sensor (2).
 7. The device as claimed inclaim 6, characterized in that the magnetic sensor (2) is a wire (7) ofnickel-iron alloy forming a closed loop and surrounded around its entirecircumference by a coil (8) that is formed by helical turns.
 8. Thedevice as claimed in claim 2, characterized in that the resistance R ofthe turn (3) of conductive material in short circuit is adjusted toobtain an L/R filtering constant, L being the inductance of the turn(3).
 9. The device as claimed in claim 3, characterized in that the turn(3) is made of soft iron (4).
 10. The device as claimed in claim 3,characterized in that the turn (3) includes, internally, a channel (6)concentric with the torus of the turn, containing the magnetic sensor(2).
 11. The device as claimed in claim 4, characterized in that theturn (3) includes, internally, a channel (6) concentric with the torusof the turn, containing the magnetic sensor (2).
 12. The device asclaimed in claim 5, characterized in that the turn (3) includes,internally, a channel (6) concentric with the torus of the turn,containing the magnetic sensor (2).